[Rd] unlink() on "~" removes the home directory

[Hervé Pagès]

On 2/26/20 14:47, Gábor Csárdi wrote:
> !!! DON'T TRY THE CODE IN THIS EMAIL AT HOME !!!

Ok I'll try it at work on my boss's computer, sounds a lot safer.

H.

> 
> Well, unlink() does what it is supposed to do, so you could argue that
> there is nothing wrong with it. Also, nobody would call unlink() on
> "~", right?
> 
> The situation is not so simple, however. E.g. if you happen to have a
> directory called "~", and you iterate over all files and directories
> to selectively remove some of them, then your code might end up
> calling unlink on the local "~" directory, and then your home is gone.
> 
> But you would not create a directory named "~", that is just asking
> for trouble. Well, surely, _intentionally_ you would not do that.
> Unintentionally, you might. E.g. something like this is enough:
> 
> # Create a subpath within a base directory
> badfun <- function(base = ".", path) {
>    dir.create(file.path(base, path), recursive = TRUE, showWarnings = FALSE)
> }
> badfun(path = "~/foo")
> 
> (If you did run this, be very careful how you remove the directory called "~"!)
> 
> A real example is `R CMD build` which deletes the home directory of
> the current user if the root of the package contains a non-empty "~"
> directory. Luckily this is now fixed in R-devel, so R 4.0.0 will do
> better. (R 3.6.3 will not.) See
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_wch_r-2Dsource_commit_1d4f7aa1dac427ea2213d1f7cd7b5c16e896af22&d=DwICAg&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=C3VCGF44o7jATPOlC8aZhaT4YGU1JtcOixJKZgu6KyI&s=iWNt-0G2gZa99bnOqNBMOHph0NyVoJdsIwuA07GhJZQ&e=
> 
> I have seen several bug reports about various packages (that call R
> CMD build) removing the home directory, so this indeed happens in
> practice to a number of people. The commit above will fix `R CMD
> build`, but it would be great to "fix" this in general.
> 
> It seems pretty hard to prevent users from creating of a "~"
> directory. But preventing unlink() from deleting "~" does not actually
> seem too hard. If unlink() could just refuse removing "~" (when expand
> = TRUE), that would be great. It seems to me that the current behavior
> is very-very rarely intended, and its consequences are potentially
> disastrous.
> 
> If unlink("~", recursive = TRUE) errors, you can still remove a local
> "~" file/dir with unlink("./~", ...). And you can still remove your
> home directory if you really want to do that, with
> unlink(path.expand("~"), ...). So no functionality is lost.
> 
> Also, if anyone is aware of packages/functions that tend to create "~"
> directories or files, please let me know.
> 
> I would be happy to submit a patch for the new unlink("~") behavior.
> 
> Thanks,
> Gabor
> 
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-- 
Hervé Pagès

Program in Computational Biology
Division of Public Health Sciences
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